Drag Coeffient monitor very high

dwilson · December 1, 2012, 16:09

I am modeling a NACA 0012 in 2D. I have drawn the aerofoil and the freestream box in NX and imported the CAD in. I then set everything up and I have set up two monitors for Cl and Cd in order to compare them to experimental data.

The Cl I have is around 1.2 which is a little high but the Cd i have is -3 and should be around 0.2. I have no idea why this is. I have set the reference values correctly I think in the monitor section (1.177 for density ref pressure is 101325 velocity is 6.943 force option is pressure +shear and the direction is set to components 0.9848,0.1736,0 as the aerofoil is simulated to be at 10 degrees. I have been looking for ages as to why the drag might be so high as I cant see anything wrong.

any throughts?

nomad · December 4, 2012, 21:14

You should resolve forces in the streamwise(drag) and normal(lift) directions since your freestream is at an alpha.

niazaliahmed · December 21, 2012, 04:56

Hi try choosing Standard K-Epsilon Low Re with adequate mesh resolution near the wall...

December 1, 2012, 16:09	Drag Coeffient monitor very high	#1
dwilson New Member anonymous Join Date: Dec 2012 Posts: 3 Rep Power: 14	I am modeling a NACA 0012 in 2D. I have drawn the aerofoil and the freestream box in NX and imported the CAD in. I then set everything up and I have set up two monitors for Cl and Cd in order to compare them to experimental data. The Cl I have is around 1.2 which is a little high but the Cd i have is -3 and should be around 0.2. I have no idea why this is. I have set the reference values correctly I think in the monitor section (1.177 for density ref pressure is 101325 velocity is 6.943 force option is pressure +shear and the direction is set to components 0.9848,0.1736,0 as the aerofoil is simulated to be at 10 degrees. I have been looking for ages as to why the drag might be so high as I cant see anything wrong. any throughts?

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December 4, 2012, 21:14		#2
nomad Member John Join Date: Aug 2009 Posts: 92 Rep Power: 17	You should resolve forces in the streamwise(drag) and normal(lift) directions since your freestream is at an alpha.

December 21, 2012, 04:56		#3
niazaliahmed New Member Niaz Ali Ahmed Join Date: Jun 2010 Posts: 14 Rep Power: 16	Hi try choosing Standard K-Epsilon Low Re with adequate mesh resolution near the wall...